Battery pack

ABSTRACT

An outer case ( 10, 20, 35, 40 ) for housing a rechargeable battery ( 1, 31, 41 ) and a battery circuit therein is composed of an upper case ( 7, 21, 42 ) and a lower case ( 8, 22, 43 ), each being formed as a half-shell body. The respective bottom faces of the upper case ( 7, 21, 42 ) and the lower case ( 8, 22, 43 ) are formed of film members ( 7   b   , 8   b   , 32, 34, 42   b   , 43   b ), and are integrally formed with resin moldings ( 7   a   , 8   a   , 33, 42   c   , 43   c ) forming circumferential side faces.

TECHNICAL FIELD

The present invention relates to a battery pack which is reduced insize, weight, and thickness so as to be used as a battery power sourcefor portable electronic equipment that is increasingly reduced in sizeas well as in thickness.

BACKGROUND ART

There is an increasing demand for reduction in size, weight, andthickness of portable information equipment and portable audio equipmentsuch as a portable telephone and a mobile computer so as to improvetheir portability. It would not be an exaggeration to state that abattery power source is the key to realize such a reduction. Inparticular, there is a strong demand for reduction in weight andthickness of a battery power source device using a rechargeable battery.

As a rechargeable battery constituting a battery power source device ofportable equipment, a nickel-cadmium battery, a nickel metal hydridebattery, and a lithium ion rechargeable battery are used. Above all, thelithium ion rechargeable battery is optimal as a power source battery ofportable electronic equipment because it has high mass energy densityand weight energy density. However, in addition to its extremely highenergy density, the lithium ion rechargeable battery uses a flammableorganic solvent as an electrolyte solution. Therefore, it is necessaryto ensure safety in the case where the battery gets into an abnormalstate. It is believed that the abnormal state is caused by anelectrical, mechanical, thermal factor, and the like. The abnormal staterefers to, for example, overcharge, short circuit, pressing, overheatingand the like. The lithium ion rechargeable battery is provided with aprotective function such as a PTC (Positive Thermal Coefficient) elementfor protecting the battery against short circuit or overheating or abattery protecting circuit for protecting the battery againstovercharge, overdischarge and the like, or a safety function such as agas exhaust vent for externally exhausting an abnormal internal pressureso as to prevent the battery from exploding. The safety function isprovided for the battery itself, whereas the battery protecting circuitor the PTC constituting the protective function is housed with thebattery in a pack case so as to be configured in a battery pack form.

FIG. 8 is an exploded view illustrating an exemplary structure of abattery pack using a flat prismatic lithium ion rechargeable battery. Alithium ion rechargeable battery 60 formed in a flat prismatic shape,and a circuit board 61 and a PTC 62, which form a battery protectingcircuit, are housed within a pack case composed of an upper case 51 anda lower case 52. Charge and discharge can be achieved through externalconnection terminals 54 provided on a side face of the lower case 52.

The reduction in thickness of portable electronic equipment isconsiderably pursued so as to improve the portability. Therefore, thereis an increasing demand for reduction in thickness of a battery packserving as a power source. In order to realize the reduction inthickness of the battery, however, a battery capacity should besacrificed. In addition, there is a limit to reduce the thickness inview of the structure of the battery.

Since there is a limit to reduce the thickness of the battery itself, athickness of a pack case is necessarily reduced so as to reduce thethickness as a battery pack. The case, which is a resin molding product,is required to have about 0.25 mm as the minimum thickness allowing themolding. The quality of a molding cannot be kept due to loweredmoldability or a degraded surface property in resin molding at theminimum thickness, thereby lowering the mass-productivity. Moreover, thethickness of the case is reduced and the like to lower the strength ofthe case. Therefore, there is a limit of the reduction in thickness soas to obtain the strength that is high enough to protect the battery andthe other components.

The present invention has an object of providing a battery pack that isreduced in thickness by using a film as a surface of a pack case, whichsurface otherwise constitutes a limit thickness of molding in resinmolding, so as to reduce a thickness of the pack case to the limit.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, the present invention is a batterypack including: one or a plurality of rechargeable batteries beingarranged in a planar manner, the rechargeable battery is housed within aflat and approximately prismatic outer case; and an external connectionterminal being connected to the rechargeable battery, the externalconnection terminal is externally exposed, wherein an arbitrary range ofat least one principal face of the outer case is formed of a filmmember, whereas the remaining part is formed of a resin molding; and theexternal connection terminal is externally exposed from an arbitraryside circumferential surface, through which the external connectionterminal is externally exposed from a portion where the resin molding isformed.

The arbitrary range is at least a region in contact with therechargeable battery.

According to the above structure, since the arbitrary range of at leastone principal face of the outer case housing the rechargeable battery isformed of the film member, a thickness of the battery pack is reduced toa thickness of the battery and the film member. Therefore, a thickness,which cannot otherwise be achieved if the entirety is formed of a resinmolding, is realized. As a result, a battery pack suitable as a batterypower source of portable electronic equipment, which is stronglyrequired to be reduced in thickness, is obtained.

Moreover, although the mass-productivity is degraded due to poormoldability of a part having a small thickness in a conventional methodusing an outer case obtained by resin molding, the mass-productivity isimproved by using the film member. Furthermore, although the principalfaces are required to satisfy both the moldability of a material and themechanical strength for the conventional outer case obtained by resinmolding, the use of film members allows the selection of a material witha high regard for the mechanical strength.

Moreover, the region other than the above-mentioned arbitrary range andthe side faces are formed of a resin molding. A material is selected forthe resin molding in consideration of the bonding ability with the filmmember, the strength, and the moldability.

Furthermore, in order to achieve the above object, the present inventionis a battery pack including: a pair of upper and lower outer cases, eachbeing formed as an approximately prismatic half-shell body by resinmolding, the outer cases are provided so as to face each other at therespective openings to be bonded at the respective open ends; one or aplurality of rechargeable batteries and a battery circuit being housedwithin the bonded outer cases; and an external connection terminal beingexternally exposed from an arbitrary side circumferential surface,wherein an arbitrary range of a part corresponding to a bottom face ofat least one of the half-shell bodies of the pair of upper and lowerouter cases is formed of a film member, whereas the remaining part isformed of a resin molding.

According the above structure, since any one of or both of the upper andlower bottom faces of the outer cases housing the rechargeable batteryand the battery circuit therein is formed of a film member, a thicknessof the battery pack is reduced to a thickness of the battery and thefilm member. Therefore, a thickness, which cannot otherwise be achievedif the entirety is formed of a resin molding, is realized. As a result,a battery pack suitable as a battery power source of portable electronicequipment, which is strongly required to be reduced in thickness, isobtained.

In the above-structure, a circumferential edge of the film member isformed by insert molding into the resin molding so that the film memberand the resin molding are integrated with each other. As a result, theouter case having high mechanical strength even at a small thickness areformed.

Moreover, when a battery pack is formed with a plurality of rechargeablebatteries, a resin molding is formed on the film member so as to fill agap formed between the rechargeable batteries arranged adjacent to eachother. As a result, since no space is formed below the film member, theplurality of rechargeable batteries and the resin molding formed on thefilm member are integrated with each other. As a result, the positionsof the housed rechargeable batteries are regulated, thereby remarkablyenhancing the strength as a battery pack.

Moreover, by forming the film member as a composite film obtained bybonding a hard film on its outer face, the part corresponding to thefilm member is restrained from being scratched, thereby improving thesurface properties and the appearance.

By forming an adhesive layer on the inner face of the film member, thefilm member is bonded to a flat face of the rechargeable battery so asto fix its position. At the same time, the film member is prevented frombeing deformed by application of a pressure.

Moreover, a reinforced plastic film, which is obtained by fixing glassfibers, carbon fibers or the like serving as a core material with anepoxy resin or the like, is used as the film member so as to enhance thestrength of the outer case.

Moreover, by forming a gas vent port through an arbitrary side face ofthe outer case, a released gas is externally exhausted when an abnormalinternal pressure is released from a gas exhaust port provided for therechargeable battery. Therefore, the outer case is not expanded. Sinceexpansion is likely to occur in the case where the larger faces of theouter case are formed of film members, the gas vent port for externallyexhausting the gas is an important requirement.

Furthermore, the battery circuit is configured with a circuit board.After the circuit board is provided on a shorter side face of therechargeable battery, the rechargeable battery and the circuit board areintegrated with each other. As a result, the operation of housing therechargeable battery and the circuit board within the outer case isfacilitated.

Furthermore, the battery circuit is configured with the circuit board.The circuit board is provided for the outer case, so that the circuitboard is fixed to the outer case. As a result, the circuit board is heldsurely. Therefore, it becomes easy to form the external connectionterminal on the circuit board and to externally expose the externalconnection terminal through an opening formed through the sidecircumferential surface of the outer case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a structure of a batterypack according to a first embodiment;

FIG. 2 is a cross-sectional view of an outer case in the structure;

FIG. 3 is a cross-sectional view of a battery pack according to a secondembodiment;

FIG. 4 is a cross-sectional view of a battery pack according to a thirdembodiment;

FIG. 5 is a cross-sectional view of a battery pack according to a fourthembodiment;

FIG. 6 is a cross-sectional view showing a step in the middle ofassembly of the battery pack according to the fourth embodiment;

FIG. 7 is a cross-sectional view showing another step in the middle ofassembly of the battery pack according to the fourth embodiment; and

FIG. 8 is an exploded perspective view showing a structure of a batterypack according to the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the accompanying drawings for understanding of thepresent invention. The following embodiment is merely an exampleembodying the present invention, and therefore does not limit atechnical scope of the present invention.

FIG. 1 shows a structure of a battery pack according to the firstembodiment. The battery pack is formed so that a flat prismatic lithiumion rechargeable battery (hereinafter, referred to as a rechargeablebattery) 1 and battery circuit components such as a circuit board 2constituting a battery protecting circuit for protecting therechargeable battery 1 from overcharge, overdischarge and the like arehoused within an outer case 10 formed by bonding an upper case 7 and alower case 8, each being formed as a half-shell body, to each other. Thebattery pack is intended to be reduced in thickness so as to meet therequirements of reduction in thickness of portable electronic equipmentfor which the battery pack is used.

In order to reduce the thickness of the battery pack, it is effective toreduce a thickness of the rechargeable battery 1. However, there is alimit to reduce the thickness of the battery so as to obtain a requiredbattery capacity. In this case, a bottom face of each of the upper case7 and the lower case 8, which are respectively formed as half-shellbodies, is made of a film member, thereby reducing the thickness of theouter case 10.

FIG. 2 is a cross-sectional view showing the upper case 7 and the lowercase 8. A bottom face of the upper case 7 formed as a half-shell body isformed of a film member 7 b, whereas a side circumferential part isformed of a resin molding 7 a. The film member 7 b is integrally formedwith the resin molding 7 a at the resin molding of the resin molding 7 aso that the entirety is formed as a half-shell body having the filmmember 7 b as a bottom face. The lower case 8 is formed in a similarmanner. A bottom face is formed of a film member 8 b. A sidecircumferential part is formed of a resin molding 8 a. The film member 8b is integrally formed with the resin molding 8 a at the resin moldingof the resin molding 8 a so that the entirety is formed as a half-shellbody having the film member 8 b as a bottom face. Although the entirebottom faces of the upper case 7 and the lower case 8 are respectivelyformed of the film members 7 b and 8 b in this case, the film member isnot necessarily provided for the entire bottom face of the lower case 8.Only the parts facing the rechargeable battery 1 may be formed as thefilm members 7 b and 8 b, and a rib for holding the board or the like isformed by resin molding at the position of the bottom face where thecircuit board 2 is provided.

PET film is suitable for the film members 7 b and 8 b. Although the PETfilm having a thickness of 50 μm or more is used, the film membershaving a thickness of 100 to 300 μm are preferable in view of ensuringof the strength as the outer case 10 or thermal effects at the resinmolding. Alternatively, PC (polycarbonate) or PMMA (methacrylate resin)is also usable as the film members 7 b and 8 b. In the case where thestrength is to be improved, a reinforced plastic film obtained by fixingglass fibers or carbon fibers serving as a core material with an epoxyresin or the like is used.

By using a composite film member obtained by forming a hard cover PETlayer on the outer face of a PET film as each of the film members 7 band 8 b, scratches are restrained from being formed so as to improve thesurface properties and the appearance. Moreover, by forming an adhesivelayer on the inner face of each of the film members 7 b and 8 b, thefilm members are bonded to flat faces of the rechargeable battery 1 soas to fix the position of the rechargeable battery 1. At the same time,when a pressure is applied onto the film member faces, deformation doesnot occur. Therefore, the fragility due to the use of the films for theexterior is eliminated.

Although PC, or PP (polypropylene) or PA (polyamide) is suitable as amaterial of molding for the resin moldings 7 a and 8 a, the material isnot limited thereto.

For the upper case 7 and the lower case 8 having the above structure,the resin moldings 7 a and 8 a are formed by resin molding after thefilm members 7 b and 8 b are inserted into a molding die. As a result,the film members 7 b and 8 b are integrated with the resin moldings 7 aand 8 b, respectively. A battery pack using the upper case 7 and thelower case 8 is assembled as follows.

In FIG. 1, an end of a negative electrode lead plate 5 is welded to abottom of a battery case 1 b, which forms a negative electrode terminalof the rechargeable battery 1. An end of a positive electrode lead plate4 is welded to a positive electrode terminal 1 a of the rechargeablebattery 1. The other end of the negative electrode lead plate 5 issoldered to a predetermined position of the circuit board 2. Thepositive electrode lead plate 4 is insulated from the battery case 1 bby an insulating paper 6. The other end of the positive electrode leadplate 4 is soldered to one electrode of a PTC element 3, whereas theother electrode of the PTC element 3 is soldered to a predeterminedposition of the circuit board 2. Since the rechargeable battery 1 andthe circuit board 2 are integrated with each other by this wiringconnection, the entirety is housed within the lower case 8. Externalconnection terminals 11 are formed on the circuit board 2. When therechargeable battery 1 and the circuit board 2 are housed within thelower case 8, the external connection terminals 11 are externallyexposed through terminal windows 8 c formed through the resin molding 8a of the lower case 8.

As shown in FIG. 2, in the side circumferential parts of the upper case7 and the lower case 8, fitting portions 12 and 13, which form steps bythe resin moldings 7 a and 8 b to fit each other, are formed. After therechargeable battery 1 and the circuit board 2 are housed within thelower case 8 as described above, the lower case 8 is capped with theupper case 7 so that their respective fitting portions 12 and 13 fiteach other. When ultrasonic vibration is vertically applied in thisstate, the upper case 7 and the lower case 8 are ultrasonically bondedto each other, thereby completing a battery pack. For theabove-described fitting portions 12 and 13, a rib portion 12 a is formedfor one of them, whereas a groove portion 13 a is formed for the other.In fitting, the rib portion 12 a fits into the groove portion 13 a sothat they are ultrasonically bonded to each other at the application ofultrasonic vibration, thereby restraining the effects on bondinginterfaces between the film members 7 b and 8 b and the resin moldings 7a and 8 a in the upper case 7 and the lower case 8, respectively.Instead of the structure in which the fitting portions 12 and 13 arerespectively provided for the resin moldings 7 a and 8 a serving as theside circumferential parts of the upper case 7 and the lower case 8 soas to be bonded through ultrasonic vibration, another structure, inwhich the resin moldings 7 a and 8 a are bonded to each other in theirside circumferential parts by claw fitting, is used.

The above-mentioned battery pack is provided with a function ofprotecting the rechargeable battery 1 against short circuit, overcharge,overdischarge, or the like. Nonetheless, if a gas is formed in therechargeable battery 1 by unexpected occurrences to abnormally increasean internal pressure of the battery, a safety vent provided for therechargeable battery 1 is activated to release the gas from therechargeable battery 1. As a result, the rechargeable battery 1 isprevented from exploding. The gas released from the rechargeable battery1 is externally exhausted through gaps between the terminal windows 8 cformed through the outer case 10 and the external output terminals 11 asgas vent ports. Therefore, the outer case 10 is never filled with thegas to be expanded. In the case where the larger faces of the outer caseare made of the film members, expansion is likely to occur. However, byexternally exhausting the gas, the deformation due to expansion isprevented. The gas vent port is also formed by providing a notch in apart of each of the ribs 12 a and the groove portions 13 a of thefitting portions 12 and 13 of the upper case 7 and the lower case 8.

The above-described battery pack is formed so as to be used forrelatively low power-consumption portable electronic equipment using asingle rechargeable battery 1, for example, a portable telephone, or adigital camera. If it is formed so as to be used for relatively highpower-consumption portable electronic equipment such as a notebookpersonal computer, a plurality of rechargeable batteries 1 is connectedin series and/or in parallel to form a battery pack.

FIG. 3 is a cross-sectional view showing a structure of a battery packaccording to the second embodiment, in which a plurality of therechargeable batteries 1 are connected in series-parallel. In this case,six flat prismatic lithium ion rechargeable batteries 1 are arranged inan array of 3 by 2 on a plane. The rechargeable batteries areelectrically connected to each other in series-parallel so as to behoused with a battery circuit within the outer case 20 to form a batterypack as the above-described battery pack.

If a cross-sectional shape of the rechargeable battery 1 is oblong asillustrated, a gap is formed between the adjacent rechargeable batteries1 in parallel arrangement. A filler resin molding 7 c is formed on thefilm member 7 b at the resin molding of the upper case 21 so as to fitinto the gap, whereas a filler resin mold 8 c is formed on the filmmember 8 b at the resin molding of the lower case 22 so as to fit intothe gap.

With the above-described structure, in the case where the plurality ofrechargeable batteries 1 are housed within the outer case 20 where thebottom faces of the half-shell bodies are formed of the film members 7 band 8 b, the area of the film members 7 b and 7 b becomes large.However, since the film members 7 b and 8 b and the rechargeablebatteries 1 are integrated with each other, the strength is restrainedfrom being lowered. Therefore, even if a pressure is applied to a partof the film members 7 b and 8 b covering the gap, deformation does notoccur. It is extremely difficult to form such a large area only by resinmolding at a similar thickness to that of the film members 7 b and 8 b.However, the film members 7 b and 8 b and the resin moldings 7 a and 8 aare integrally molded as in this structure, thereby achieving thereduction of the thickness of the outer case 10.

FIG. 4 is a cross-sectional view showing a structure of a battery packaccording to the third embodiment. A plurality of cylindricalrechargeable batteries 41 are arranged in parallel so as to be housedwith a circuit board not shown within an outer case 40, thereby forminga battery pack. In FIG. 4, even in the case where the rechargeablebattery 41 is a cylindrical battery, gaps are also formed above andbelow the batteries between the adjacent batteries. A filler resinmolding 42 c is formed on a film member 42 b at the resin molding of anupper case 42 so as to fit into the gap, whereas a filler resin molding43 c is formed on a film member 43 b at the resin molding of a lowercase so as to fit into the gap. The formation of the filler resinmoldings 42 c and 43 c prevents the strength from being lowered even ifthe area of the film members 42 b and 43 b becomes large because therechargeable batteries 41 and the film members 42 b and 43 b areintegrated with each other. The deformation does not occur either in thecase where a pressure is applied to the film members 42 b and 43 bcovering the gaps.

FIG. 5 is a cross-sectional view of a battery pack according to thefourth embodiment. A flat prismatic rechargeable battery 31 is housedwith a circuit board not shown within an outer case 35 to form a batterypack. The battery pack is characterized by a method of forming the outercase 35.

FIG. 6 shows a state where the flat prismatic rechargeable battery 31and battery circuit components (not shown) such as a battery protectingcircuit for protecting the rechargeable battery 31 against overcharge,overdischarge and the like and a circuit board, on which externalconnection terminals are formed, are provided within a resin molding 33which is molded in advance. The resin molding 33 has such a structurethat, for example, it is divided into four so as to correspond to fourside circumferential surfaces. After the rechargeable battery 31 and thebattery circuit components are provided inside the resin molding, theyare integrated with each other. Moreover, the resin molding 33 isprovided with terminal windows (not shown) through which the externalconnection terminals are externally exposed. This state is also achievedby first integrating the rechargeable battery 31 and the battery circuitcomponents with each other, followed by the formation of the resinmolding 33 in the side circumference parts by a method such as resinmolding. In this manner, in the state where the rechargeable battery 31and the battery circuit components are provided within the resin molding33, film members 32 and 34 are provided to face upper and lower flatsurfaces. When the resin molding 33 and the film members 32 and 34 areintegrated with each other by, for example, laser welding, ultrasonicwelding or the like, a battery pack shown in FIG. 5 is completed. Thelaser welding is advantageous in its facility of control of weldingstrength because the welding of a portion to be welded is ensured. Inaddition, a trace of the welding is hardly varied. Moreover, if anadhesive layer is formed on a surface of each of the film members 32 and34 in contact with the rechargeable battery 31, the rechargeable battery31 and the film members 32 and 34 are integrally formed so as to furtherenhance the strength as the battery pack.

Both the upper and lower film members 32 and 34 are integrated with theresin molding 33 at the last step in the above description. However, thebattery pack shown in FIG. 5 is also formed by integrally forming theresin molding 33 with any one of the film members, for example, the filmmember 34 so that the other film member 32 is integrated with the resinmolding 33 in the state where the battery circuit components and therechargeable battery 31 are provided within the resin molding 33.

FIG. 7 shows a state where the rechargeable battery 31 and batterycircuit components (not shown) are integrated with each other so thatthe film members 32 and 33 are provided to face the upper and lower flatfaces. If the side circumference of the resin molding 33 is formed byresin molding or the like in this state, the film members 32 and 34 andthe resin molding 33 are integrated with each other to complete thebattery pack shown in FIG. 5.

INDUSTRIAL APPLICABILITY

According to the present invention, since the bottom faces of the caseformed in a flat shape are made of film members, the outer case isreduced in thickness, thereby allowing the formation of a thin batterypack. Accordingly, the present invention is suitable to provide abattery pack meeting the requirements of reduction of the thickness ofportable electronic equipment.

1. A battery pack including: one or a plurality of rechargeablebatteries arranged in a planar manner, the rechargeable battery beinghoused within a flat and approximately prismatic outer case; and anexternal connection terminal connected to the rechargeable battery, theexternal connection terminal being externally exposed, wherein anarbitrary range of at least one principal face of the outer case isformed of a film member, whereas the remaining part is formed of a resinmolding; and the external connection terminal is externally exposed froma portion where the resin molding is formed.
 2. A battery packincluding: a pair of upper and lower outer cases, each being formed asan approximately prismatic half-shell body by resin molding, the outercases being provided so as to face each other at the respective openingsto be bonded at the respective open ends; one or a plurality ofrechargeable batteries and a battery circuit housed within the bondedouter cases; and an external connection terminal being externallyexposed from an arbitrary side circumferential surface, wherein anarbitrary range of a part corresponding to a bottom face of at least oneof the half-shell bodies of the pair of upper and lower outer cases isformed of a film member, whereas the remaining part is formed of a resinmolding.
 3. The battery pack according to any one of claims 1 and 2,wherein a circumferential edge of the film member is formed by insertmolding into the resin molding.
 4. The battery pack according to any oneof claims 1 and 2, wherein the resin molding is formed on the filmmember so as to fill a gap formed between the rechargeable batteriesarranged adjacent to each other when the plurality of rechargeablebatteries are arranged.
 5. The battery pack according to any one ofclaims 1 and 2, wherein the film member is formed as a composite filmobtained by bonding a hard film on its outer face.
 6. The battery packaccording to any one of claims 1 and 2, wherein an adhesive layer isformed on the inner face of the film member.
 7. The battery packaccording to any one of claims 1 and 2, wherein the film member is areinforced plastic film having a core material in a resin.
 8. Thebattery pack according to any one of claims 1 and 2, wherein a gas ventport is formed in the resin molding of the outer-case.
 9. The batterypack according to claim 1, wherein a battery circuit is configured witha circuit board, and the circuit board is provided on a shorter sideface of the rechargeable battery.
 10. The battery pack according toclaim 2, wherein the battery circuit is configured with a circuit board,and the circuit board is provided on a shorter side face of therechargeable battery.
 11. The battery pack according to any one ofclaims 9 and 10, wherein the external connection terminal is formed onthe circuit board and the external connection terminal is externallyexposed through an opening formed through the side circumferentialsurface of the outer case.
 12. The battery pack according to claim 1,wherein a battery circuit is configured with the circuit board, and thecircuit board is provided for the outer case.
 13. The battery packaccording to claim 2, wherein the battery circuit is configured with thecircuit board, and the circuit board is provided for the outer case. 14.The battery pack according to any one of claims 12 and 13, wherein theexternal connection terminal is formed on the circuit board and theexternal connection terminal is externally exposed through an openingformed through the side circumferential surface of the outer case.